With the development of automobiles having high fuel efficiency and light weight, automobile components have been continuously produced to have high strength. In addition, some parts of automobiles are required to have high strength and other parts are required to have high fracture toughness.
Particularly, steel sheets for automobiles are generally formed through pressing and thus require high ductility (elongation) to guarantee high press formability.
In the related art, high strength cold-rolled steel sheets having a tensile strength of 700 MPa to 1,200 MPa are not used in manufacture of complicated components for automobiles at room temperature due to a formation limit resulting from low ductility thereof, and when hot stamping is performed to overcome this problem, pressing is carried out at high temperature to provide improved formability, thereby enabling manufacture of complicated components. However, hot stamping causes significant variation in physical properties of the steel sheets. Particularly, after hot stamping, a conventional high strength cold-rolled steel sheet having a tensile strength (TS) of 700 MPa to 1,200 MPa has slightly increased strength, but has a significantly reduced elongation of 10 wt % or less, causing brittle fracture upon collision, thereby deteriorating impact stability.
In the related art, Korean Patent Publication No. 10-0723159 (Issue Date: 2007 May 30) discloses a cold-rolled steel sheet having excellent formability and a method for manufacturing the same.